This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A278597 #15 Jun 29 2017 11:46:43 %S A278597 1,2,2,2,3,2,2,3,3,2,2,3,3,3,2,2,3,3,3,3,2,2,3,3,3,3,3,2,2,3,3,3,3,3, %T A278597 3,2,2,3,3,3,3,3,3,3,2,2,3,3,3,3,3,3,3,3,2,2,3,3,3,3,3,3,3,3,3,2,2,3, %U A278597 3,3,3,3,3,3,3,3,3,2,2,3,3,3,3,3,3,3,3,3,3,3,2,2,3,3,3,3,3,3,3,3,3,3,3,3,2 %N A278597 One half of A278481. %C A278597 Apart from the left border and the right border, the rest of the elements are 3's. %F A278597 a(n) = A278481(n)/2. %e A278597 The sequence written as a triangle begins: %e A278597 1; %e A278597 2, 2; %e A278597 2, 3, 2; %e A278597 2, 3, 3, 2; %e A278597 2, 3, 3, 3, 2; %e A278597 2, 3, 3, 3, 3, 2; %e A278597 2, 3, 3, 3, 3, 3, 2; %e A278597 2, 3, 3, 3, 3, 3, 3, 2; %e A278597 2, 3, 3, 3, 3, 3, 3, 3, 2; %e A278597 2, 3, 3, 3, 3, 3, 3, 3, 3, 2; %e A278597 ... %Y A278597 Row sums give A016777. %Y A278597 Left border gives A040000, the same as the right border. %Y A278597 Middle column gives A122553. %Y A278597 Every diagonal that is parallel to any of the borders gives the elements greater than 1 of A158799. %Y A278597 Cf. A278481. %K A278597 nonn,tabl %O A278597 1,2 %A A278597 _Omar E. Pol_, Nov 23 2016